Arc Strike on ASME VIII U-stamped Vessel

[bradlebj]

I have an ASME Section VIII vessel that was fabricated and U-stamped in accordance with the 2001 edition of the code. It was shipped by the vendor to a module assembly shop, contracted by my company, and then sent to our site. Post receipt, it was noted that the vessel has several arc strikes that we plan on removing by grinding. I indicated the travel path simply to note that we don't actually know when the arc strike occurred.

NBIC Interpretation 98-30 notes that grinding operations that reduce the outside diameter, length, and thickness of a pressure retaining item are not considered alterations and are not required to be performed by a holder of an "R" Certificate of Authorization, provided the changes do not affect the pressure-containing capabilities of the vessel.

ASME PCC-2, Article 3.4, Section 4.1.3 requires NDE to be performed following the removal of a flaw or defect. We will also need to perform UT to verify that min wall is not violated after defect removal.

Two questions on this situation:
1. Does the subsequent NDE need to be performed by a holder of an "R" Certificate of Authorization?
2. What involvement, if any, is required by an Authorized Inspector certified by the National Board?

 

[metengr]

1. No, not necessarily. You are removing the arc strike mechanically and confirming no cracks using NDT. There is no need for an R-Certificate Holder unless weld repair is necessary to restore wall thickness.

2. None unless weld repair is required to restore the wall thickness.

 

[racookpe1978]

You do need to confirm by surface NDE that there are no subsequent cracking. And the removal cannot cut through the PV wall obviously. Surface grinding will not do that, but for example, an arc strike that is carelessly ground out on a mating flange might cause a leakage path.

 

[metengr]

Surface grinding can and will remove arc strikes. The question is depth after grinding to ensure all heat affected material has been removed as a result of the arc strike. Again, an R-Certificate holder is not necessary until such time the final depth falls below min wall and weld repair is necessary.

You may need to confirm the removal of heat affected material by etching or hardness testing.

 

[r6155]

What happened with the visual inspection during fabrication?
Regards
r6155

 

[bradlebj]

There is nothing noted in the quality data package in regards to unacceptable marks from the vendor shop. And having dealt with this vendor previously, they have in the past questioned the need to remove arc strikes (Section VIII alone is silent on arc strikes). So between that, and the programmatic lack of receipt inspection activities here and at our module fab facility, I don't have good information on how or when these arc strikes occurred.

 

[DVWE]

Section VIII alone is silent on arc strikes

Not necessarily. Section IX defines an arc strike as an "inadvertent discontinuity..."

It's up to your company to define an arc strike as a defect in your specifications. See the definitions of defect and discontinuity per section IX.

My thoughts on vendors that question the need to remove arc strikes are that they need a good education on the potential problems arc strikes may cause, and leaving them on a pressure vessel just screams of lack of workmanship.